Cloning of porcine proglucagon and effect of commensal bacteria on relative gene expression in the intestine of gnotobiotic pigs

Abstract

Porcine proglucagon mRNA sequence was determined by designing primers based on homologous regions in bovine and human genes. The porcine sequence shared 90% nucleotide identity with human proglucagon; however, predicted Ser159Arg and Leu160Lys substitutions were observed. This newly identified sequence suggests that the intestinal trophic peptide, glucagon-like peptide 2 (GLP-2), is actually 35 amino acids in the pig rather than 33 amino acids, as previously reported. To determine the effect of different bacteria on intestinal proglucagon gene expression, 16 piglets were reared in gnotobiotic isolators maintained germ-free (GF), monoassociated with Lactobacillus fermentum (LF) or Escherichia coli (EC), or conventionalized (CV) in two separate experiments for 13 d. Cultured cecal contents confirmed microbial status with the exception of GF pigs in exp. 2, which were contaminated with Staphylococcus epidermidis (SE). Mean fold differences in ileal proglucagon expression (CV set to 1) were 1.0ab, 1.6a, 0.7b, 1.0ab for GF, LF, EC and CV in exp. 1 and 4.0a, 2.0b, 0.6c, 1.0c for SE, LF, EC and CV groups in exp. 2, respectively. This study, for the first time, accurately describes the full nucleotide sequence for porcine proglucagon, and shows that proglucagon expression is differentially regulated by bacteria colonizing intestine of neonatal piglets. Key words: Proglucagon, gnotobiotic, pig, gene expression, intestine